Various bacterial strains were tested for their ability to stimulate immunoglobulin A (IgA) plasmocytes to populate the duodenal lamina propria in axenic mice.The mice were associated with the strains for at least 4 weeks. The strains 532 on August 5, 2020 by guest http://iai.asm.org/ Downloaded from

Fourteen microbial strains isolated from conventional rats were inoculated into axenic rats and mice receiving identical diets. The populations of these organisms which became established in the feces of gnotobiotic adult recipient rats and mice were quite similar. The only major difference was that one strain, belonging to the genus Clostridium, disappeared from the feces of gnotobiotic mice, whereas this strain became established in gnotobiotic rats. Most of the strictly anaerobic strains were absent or present only in small numbers before weaning in young rats and mice. A clear-cut barrier effect against Salmonella typhimurium was found in adult gnotobiotic mice colonized with a complex flora derived from a conventional chicken. The microflora established in these recipient mice exerted the same barrier effect when further transferred into axenic chickens. Inoculation of feces from a human donor into adult gnotobiotic recipient mice produced colonization by several strains from the donor, whereas other strains, belonging to the genera Bifidobacterium, Lactobacillus, and Clostridium were present in the donor, but did not persist in recipient mice. In these mice, nonetheless, the colonizing human fecal flora exerted an effective barrier against a toxigenic strain of Clostridium difficile. This barrier effect spontaneously disappeared several weeks later. Administration of clindamycin to the recipient mice led to large variations in the number of viable cells of C. difficile.

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Oral preventive treatment of gnotobiotic mice by Saccharomyces boulardii significantly decreased mortality following Clostridium difficile infection. A single S. boulardii ingestion protected 16% of mice, whereas 56% were protected when S. boulardii was given continuously in the drinking water. No direct antagonistic effect of the yeast on C. difficile numbers was detected, whereas a modulation of fecal cytotoxin production was demonstrated.

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